What component is commonly used to change 120V AC house current to a lower AC voltage for other uses?

The component commonly used to change 120V AC house current to a lower AC voltage is a transformer. A transformer operates on the principle of electromagnetic induction and is specifically designed to step up or step down AC voltage levels. It consists of two coils of wire, known as the primary and secondary windings, which are magnetically coupled.

When alternating current flows through the primary winding, it generates a varying magnetic field that induces a voltage in the secondary winding. The ratio between the number of turns in the primary winding and the secondary winding determines the change in voltage. For instance, if the secondary winding has fewer turns than the primary, the output voltage will be lower, effectively converting the higher 120V AC into a lower AC voltage suitable for various applications.

Other components serve different functions; for instance, a variable capacitor is used primarily in tuning circuits, while a transistor is mainly employed for switching and amplification tasks. A diode, on the other hand, is utilized for rectification processes to convert AC into DC or to allow current to flow in only one direction. Understanding these functionalities clarifies why the transformer is the appropriate choice for this specific application.